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Simple tablet charge controller using Sonoff’s ZBMini

I’m using an Amazon tablet stuck to my fridge with several magnets and 3D printed case as a dashboard.

I read it’s bad for the tablet’s battery if it’s constantly plugged into a charger. Battery can swallow or worse.

So I installed Sonoff’s #ZBMini (Zigbee) smart switch into a socket where the charger is connected.

Added it to Zigbee2MQTT and created 2 simple automations:

  1. turn off the charger if the tablet battery charge drops below 20% (image below) and
  2. turn on the charger if the tablet battery charge is above 80%
screenshot home assistant automation turn on smart switch

I had to wait for more than a week for a battery to discharge and then automation triggered:

home assistant chart - battery charge, discharge

It needed 3 hrs to charge the battery from 20% to 80%.

Good. I hope this mechanism will prolong the life of the tablet battery.

I only wonder why tablets don’t manage this kind of charging / discharging control by themselves.

Comments

7 responses to “Simple tablet charge controller using Sonoff’s ZBMini”

  1. Martin Pugh Avatar
    Martin Pugh

    @tomi I do something similar. We have a couple of fire tablets. They are both powered through Zigbee smart sockets and turn on/off as needed using the same 20/80 rules.

  2. Martin Pugh Avatar
    Martin Pugh

    @tomi I forgot to mention, if you haven't already, it's worth including a trigger in your automations for home assistant startup. I missed this and had the automation trigger with exactly 20 and 80 percent but if home assistant happens to restart at just the wrong time (because I'm adding extra stuff) I missed the exact 20/80 so the automation didn't trigger.

  3. hindsholm Avatar
    hindsholm

    @tomi I use a Lenovo tablet for the same purpose and it actually has a setting for when it is constantly connected to a charger.

  4. OBELIKS Avatar
    OBELIKS

    @tomi Usually you can limit the maximum charge. At least on Samsung devices.
    But this solution might be even better. Maybe you can do something similar with Tasker.

  5. ZS Avatar
    ZS

    @tomi Real tablets do. Amazon ewaste Fire tabs don’t, because they’re running on some prehistoric version of Android.

    iPads and Samsung tablets have “always powered” routines, and even the junk Lenovo 8” tablet has something similar (it has a Dorito for a CPU and I got it for £30 off Amazon Warehouse).

  6. Peter Mount Avatar
    Peter Mount

    @tomi There are some devices which have an option to set the max amount of charge – it varies by manufacturer.

    e.g. my phone has it but I just checked one of my Amazon tablets and couldn't see the option.

    I believe there are some apps available to do this but not tried it.

    I really should look into this as I have 2 tablets setup like this – mounted on walls

    1. Tomi the Slav and 1024 others Avatar
      Tomi the Slav and 1024 others

      @peter @tomi Thanks, I've checked too and it seems my Amazon's FireHD 10 tablet does not have this option.

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